1. Field of the Invention
This invention relates to the use of 3-acylamino-1,2,4-triazoles and 1-acyl-3-amino-1,2,4-triazoles and mixtures thereof as corrosion inhibitors for non-ferrous metals in aqueous systems, oils and oil-containing emulsions.
2. Statement of Related Art
By virtue of their relatively high corrosion resistance, non-ferrous metals, for example copper or zinc, or alloys containing them, such as brass or bronze, are preferentially used as industrial materials. The surfaces of metals such as these are corroded in industrial processes where they come into contact with oils or oil-containing aqueous emulsions, in some cases under extreme temperature and pressure conditions. Examples of such processes are industrial cooling processes, surface cleaning processes for metals and processes for machining metal surfaces, such as drilling, cutting, rolling, etc. Although oils or oilcontaining emulsions are used in processes such as these, the effect of water on the metal surface cannot be completely avoided. Moreover, the successive corrosion of the metal parts coming into contact with the oils or oil-containing liquids distinctly shortens the useful life of the machines involved and leads to problems in the subsequent treatment of the metal surface.
In addition, non-ferrous metals of the type in question are preferentially used in the construction of water-carrying installations, such as steam-generation plants, heating systems, cooling water circuits, and the like. They are of particular significance as condenser-tube materials in steam-powered electricity generating stations. However, despite their relatively high resistance to corrosion, analytically detectable quantities of the high-quality materials, particularly copper, are unavoidably leached by the water flowing through under normal conditions. Traces of copper in particular accumulate on subsequent cooling water pipes of steel or other less noble metals or metal alloys where they lead to - in some cases disastrous - pitting corrosion.
For this reason, additional treatment of the water coming into contact with the non-ferrous metals to reduce this erosion of metal is of technical importance. In practice, there are very few inhibitors suitable for this purpose; these inhibitors are essentially mercaptobenzthiazole, benzotriazole, tolyl triazole, and benzimidazole. These compounds are relatively effective as copper inhibitors but are attended by numerous disadvantages. Thus, in chemical terms, they are relatively difficult to obtain and, because of this, can only be used to a limited extent on economic grounds. Another disadvantage of the compounds mentioned is their very poor solubility at acidic pH-values, with the result that considerable difficulties are involved in the blending of these products, particularly in concentrate form, for practical application. In addition, these concentrates are generally not sufficiently stable in storage. Another disadvantage is that, in some cases, the compounds mentioned and their derivatives are highly toxic and, accordingly, are prohibited in certain fields of application.
U.S. Pat. No. 4,298,568 (corresponding to published German patent application 29 34 461) as well as published European patent application 25,863 describe the use of 3-amino-5-alkyl-1,2,4-triazoles to inhibit the corrosion of non-ferrous metals in aqueous raw-water systems. These compounds certainly show better performance properties than the above-mentioned corrosion inhibitors and, in addition, are relatively easy to obtain.
However, a crucial disadvantage of the foregoing compounds is that they are produced from a carboxylic acid by reaction with aminoguanidinium hydrogen carbonate in a condensation reaction which can only be catalyzed with hydrochloric acid. The use of any other mineral acid, for example phosphoric acid, results in poor yields of alkylaminotriazole. Since the hydrochloric acid used as catalyst is known to have a highly corrosive effect upon the equipment and reaction vessels used, the condensation reaction can only be carried out in specially protected vessels or using suitable apparatus, such as enamel reactors, enamel-lined cooling systems, etc., which are difficult or in some instances impossible to obtain and which involves considerable effort and expense. For efficiency as well as economy, therefore, a search has been conducted for other, more safe and less expensive readily obtainable compounds which may be used as corrosive inhibitors for non-ferrous metals.
German patent application 35 19 522 (published Dec. 4, 1986, subsequent to the German priority application of the present invention) describes the use of 1,2,4-triazole derivatives in which the alkyl moiety in the 5-position of the heterocyclic ring is terminally hydroxylated. The disadvantages of previously known triazole derivatives, such as their poor solubility in water at acidic pH-values, are eliminated in this way. Unfortunately, the corrosion-inhibiting effect of compounds such as these falls far short of requirements.